1. Field of the Invention
This invention relates to a hydrostatic starter device for an internal combustion engine to start the internal combustion engine from a stop. The starter device has a hydrostatic power unit that is in a drive connection with the output shaft of the internal combustion engine, is in communication with a hydraulic accumulator, and is driven with hydraulic fluid from the hydraulic fluid accumulator to start the internal combustion engine.
2. Description of Related Art
On internal combustion engines, such as diesel or gasoline engines, starter devices driven by an electric motor are generally used. To start the internal combustion engine, the speed of rotation necessary for the self-sustaining running of the internal combustion engine is produced with an electric starter motor connected by a transmission with the crankshaft of the internal combustion engine. The transmission is generally formed by a pinion gear on the output shaft of the electric starter motor and a ring gear on the crankshaft of the internal combustion engine, and has a high translation ratio so that a high-speed and compact electric starter motor can be used.
To reduce the fuel consumption of the internal combustion engine during pauses or interruptions in operation, it is known that a start-stop function for the internal combustion engine can be provided, in which the idling internal combustion engine is shut off during pauses or interruptions in work and is automatically restarted when there is a request for torque. The shutdown and subsequent restarting of the internal combustion engine can occur even with relatively brief idle times, so that the starting process of the internal combustion engine must be carried out correspondingly frequently and at brief intervals during the operation of the internal combustion engine. This requirement places high demands on the starter device of the internal combustion engine with regard to endurance strength and the ability to supply the starting energy required to start the internal combustion engine.
On known starter devices operated with electric motors with a high-speed and compact electric starter motor, very strong currents are required to flow for a short period of time to start the internal combustion engine to produce the torque necessary to start the internal combustion engine. The currents that are generated to start the internal combustion engine result in a significant rise in temperature. If the internal combustion engine is to be restarted after short intervals for a start-stop function, this operating behavior results in the overheating of known starter devices operated with an electric motor and leads to the failure of the electric starter motor and, thus, of the starter device operated by the electric motor. To be able to actuate a conventional starter device of this type driven by an electric motor with an electrical starter motor for a start-stop function at brief intervals, the level of the electrical voltage must be increased and the electrical starter motor must be designed so that it has a correspondingly high fatigue strength. This results in a significant increase in the design effort and manufacturing costs required.
Known start-stop functions are associated with a hybridization of the drive train driven by the internal combustion engine, as a result of which the starting of the internal combustion engine and the increase in the speed of the internal combustion engine can occur in a short period of time. However, for a start-stop function of this type as part of a hybridization, additional components in the drive train are necessary in the form of an electrical flywheel-type motor or generator, a high-performance battery, a performance control module in the form of power electronics, and an electronic control system, as a result of which a start-stop function of this type requires significant extra construction effort and not insignificant extra costs.
DE 10 2008 028 547 A1 and EP 2 308 795 A1 describe internal combustion engines with a hydrostatic starter device in which a hydrostatic power unit is operated with hydraulic fluid from a hydraulic fluid accumulator to start the internal combustion engine. To eliminate the additional construction effort and expense for a starter device operated by an electric motor on the internal combustion engine, it must be ensured that the hydraulic fluid accumulator is charged before the internal combustion engine is shut off and/or that the hydraulic fluid accumulator can be charged while the internal combustion engine is shut off. In this regard, EP 2 308 795 A1 discloses an auxiliary charging device that can be used to charge the hydraulic fluid accumulator. In DE 10 2008 028 547 A1 and EP 2 308 795 A1, a hydraulic work pump in the drive train driven by the internal combustion engine, which supplies corresponding users of a hydraulic work system of a vehicle with hydraulic fluid, forms the hydrostatic power unit of the hydrostatic starter system. The hydraulic work pump can be operated as a hydraulic motor and, to start the internal combustion engine, is driven in operation as a motor by hydraulic fluid from the hydraulic fluid accumulator. However, the hydraulic work pump is rigidly coupled with the crankshaft or an output shaft of the internal combustion engine so that the hydraulic work pump is also driven after the start of the internal combustion engine. In this case, with known hydrostatic starter devices, high idle losses occur, in particular under operating conditions in which no users of the hydraulic work system are actuated.
An object of this invention is to provide a hydrostatic starter system of the general type described above but with which a start-stop function of the internal combustion engine can be provided in a rugged and economical construction, and the idle losses that occur during the operation of the internal combustion engine are reduced.